1
It is necessary to mention certain relationships observed in the H NMR spectra of the series of
synthesized aldimines (Table 2). The presence of the methyl group in the heteroaromatic ring leads to an upfield
shift of the signal for CH=N compared with the unsubstituted molecules. All the thiophene imines are
characterized by larger chemical shifts of the signals for the protons of the CH=N and CH3 groups than in the
corresponding furan compounds.
In numerous investigations (see the reviews [6-9] and also the papers [10-13]) it was shown that
silylation of the CH=N double bond leads mainly to the formation of N-silylated products. Recently we found
for the first time [14] that addition of the silyl group to the carbon atom of the imine bond CH=N also occurs in
addition to N-silylation in the reaction of alkylhydrosilanes with furan, thiophene, and pyridine methylene-
ortho-trifluoromethylanilines. In this connection it seemed of interest to investigate the hydrosilylation of the
newly synthesized azomethines 3a-d containing a fluoro group at the ortho position of the aza part of the
molecules.
Earlier [11, 14] we found that one of the most active catalysts for the hydrosilylation of heterocyclic
imines is the dimeric complex of monovalent palladium bis{[µ-chloroallyl]palladium} [Pd(allyl)Cl]2. The
reaction of the new furan and thiophene aldimines 3a-d with triethylsilane in the presence of this complex was
studied. The reactions were conducted in benzene at 65°C with the optimum substrate–silane ratio 1:1.2 mol and
a catalyst concentration of 2 mol %. The reaction was monitored by TLC and GLC-MS. On completion of
silylation (the reaction times are given in Table 4) the reaction mixture was treated (as indicated in the
experimental section) and analyzed by 1H NMR.
1
In the H NMR spectra of the reaction mixtures there are sets of signals that indicate the formation of
several types of products containing central CH2–HN, CH2–NSiEt3, Et3SiCH–NH, and CH=N groups. These
compounds are characterized by a signal for CH2 and a broad singlet for NH (2H and 1H), a singlet for CH2
(2H), two broad singlets for the protons of the CH–NH group (1H–1H), and a singlet in the region of CH=N
respectively (Table 4). The signals for the protons of the (hetero)aromatic rings of all the obtained compounds
are in the characteristic regions of the spectra. The SiEt3 group appears in the 1H NMR spectra of the synthesized
silyl compounds in the form of two groups of signals for the protons of the CH2 (6H, q) and CH3
TABLE 2. The 1H NMR Spectra of the Imines 3a-l
Com-
pound
Chemical shifts, δ, ppm (SSCC, J, Hz)
CH=N, s CH3, s
Ring protons
3a
8.40
—
6.60 (1H, dd, J = 2.0, J = 3.6, H-4); 7.0-7.5 (5Н, m, H-3,3',
H-4',5',6'); 7.68 (1H, m, H-5)
3b
3c
3d
8.26
8.63
8.53
2.44
—
6.21 (1H, d, J = 3.2, H-4); 7.0-7.4 (5Н, m, H-3,3',4',5',6')
7.0-7.2 (5Н, m, H-4,3',4',5',6'); 7.5 (1H, m, H-3,5)
2.56
6.83 (1H, d, J = 3.0, H-4); 7.0-7.2 (3Н, m, H-3,4',5'); 7.3 (1Н, m,
H-3'); 7.46 (1Н, m, H-6')
3e
3f
8.28
8.18
8.54
—
2.45
—
6.59 (1H, dd, J = 1.8, J = 3.4, H-4); 6.8-7.2 (4Н, m,
H-3, 2',4',5'); 7.35 (1Н, m, H-6'); 7.65 (1H, s, H-5)
6.23 (1H, d, J = 2.0, H-4), 6.8-7.2 (4Н, m, H-3,2',4',5');
7.35 (1Н, m, H-6')
6.8-7.1 (3Н, m, H-2',4',5'); 7.15 (1Н, m, J = 4.6, H-4);
7.35 (1Н, m, H-6'); 7.56 (2H, m, H-3,5)
3g
3h
3i
8.43
8.25
2.55
—
6.7-7.1 (4Н, m, Н-4,2',4',5'); 7.2-7.5 (2Н, m, H-3,6')
6.55 (1H, dd, J = 2.0, J = 3.6, H-4); 6.93 (1Н, d, J = 3.6, H-3);
6.9-7.1 (2Н, m, H-2',6'); 7.1-7.3 (2Н, m, H-3',5'); 7.60 (1H, m, H-5)
3j
8.14
2.42
6.16 (1H, d, J = 2.8, H-4); 6.82 ( 1Н, d, J = 2.8, H-3);
7.0-7.1 (2Н, m, H-2',6'); 7.1-7.3 (2Н, m, H-3',5')
3k
3l
8.54
8.48
—
7.0-7.3 (5Н, m, H-3,4,5,2',6'); 7.5-7.6 (2Н, m, H-3',5')
2.57
6.87 (1Н, br. s, Н-4); 7.0-7.2 (2Н, m, H-2',6');
7.2-7.5 (2Н, m, H-3',5'); 7.6 (1Н, br. s, H-3)
1114